Today, head-up displays (HUDs) are commonly used in vehicles. Current HUDs can be categorized into two groups: windscreen HUD and combiner HUD. The former uses the windscreen of vehicle as a projection surface, while the later uses an additional combiner screen as the projection surface. The combiner screen HUDs are superior to the windscreen HUDs in means of over-all costs, and in addition, the combiner HUDs can be easily sold as aftermarket products in a one-box design.
However, the combiner HUD has the particular drawback of their smaller screen size of the projection surface. This may lead to a smaller text and symbol size or less information to be displayed on the combiner screens. Furthermore, the display of the combiner HUD usually cannot use its total surface for the projection because it must compensate for movements of the driver's head.